This invention relates to catheter-inserted medical and surgical devices, and is more particularly concerned with a balloon pump that is inserted into the aorta of a patient to enhance cardiac output and increase perfusion.
An intra-aortic balloon pump, or IABP, is a sausage-shaped balloon that is positioned in a patient""s artery and is timed with the cardiac cycle to inflate during diastole (i.e., when the ventricle relaxes for filling) and to deflate during systole (i.e., when the ventricle contracts for pumping). The IABP is typically non-distensible and made of a polyurethane film.
The purpose of the IABP is to reduce left ventricular preload and afterload. This can reduce the pulmonary capillary wedge pressure by approximately 20%, and can decrease aortic systolic pressure by 10% to 20%. With the IABP in place, mean arterial pressure can increase by 30 to 40% secondary to enhanced diastolic blood pressure, and both cardiac output and stroke volume experience a moderate increase.
The IABP supports the heart by pressure unloading by means of volume displacement, but not from volume unloading. There can be up to 15% improvement in myocardial energy balance, depending on diastolic augmentation, left ventricular endiastolic pressure (filling during diastole), proper timing, balloon size, and coronary resistance.
The typical LABP has polyurethane double-lumen catheter, 8.5 F to 10.5 F, with a balloon with a capacity of 30 cc to 50 cc, and a pressure transducer mounted at the tip. The IABP is percutaneously inserted via a guidewire through the iliac artery, and is placed in the descending aorta above the renal arteries. Fluoroscopy is used to guide placement of the unit at this position.
An extracorporeal pumping unit inflates and deflates the catheter lumen with a suitable neutral drive gas, such as helium. Electrocardiograph leads provide timing information, such as the R wave, to estimate systole and the sensor at the catheter tip provides arterial waveforms, and these are used to time the inflation and deflation, and to assess the hemodynamic effects of the IABP.
The IABP may be indicated for several conditions, i.e., cardiogenic shock; as an adjunct to thrombolysis or PTCA (percutaneous transluminal coronary angioplasty) in AMI (acute myocardial infarction) to maintain vessel patency; prior to coronary artery bypass graft surgery in high risk patients; severe mitral regurgitation (mitral valve too loose); decompensated mitral stenosis (mitral valve too tight); as a bridge to transplant (if an organ is readily available); refractory congestive heart failure; mechanical complication of AMI, i.e., mitral regurgitation due to papillary involvement or ventricular septal defect; or unstable angina refractory to medical therapy.
The current IABP, in which a single balloon inflates, is bi-directional, that is, it pushes some of the blood forward, perfusing to the lower body, and also pushes some of the blood towards the aortic root. This has been considered as increasing blood flow into the arteries near the aortic root, i.e., to the coronary arteries. However, this device can cause other problems, as indicated below.
Complications can result when the IABP is employed, most commonly vascular problems, such as limb ischemia, compartment syndrome, mesentaeric infarction, aortic perforation or dissection. Other complications include balloon rupture, passage failure, thrombosis, and infection. Risk factors include peripheral vascular disease, diabetes myelitis, and tobacco use (smoking).
Contraindications include significant aortic insufficiency; aortic aneurysm/dissection; sepsis; peripheral vascular disease; atrial septal defect; patent foramen ovale; patent ductus arteriosi; or coagulopathy. Use is also contraindicated if there is no defined endpoint of revascularization or transplant.
With the current IABP the patient is confined to strict bed rest, with no hip flexion permitted beyond about 10-20 degrees.
A stiff aorta, which can be secondary to atherosclerosis, may prevent lateral distribution of inflation pressure with a conventional IABP, and resulting in a low intra-aortic pressure change. Aortic regurgitation, or AR, is a contraindication for a conventional IABP, because of the reverse pumping action.
A balloon pump of this general type is described in Milder et al. U.S. Pat. No. 4,902,272. In the Milder et al. patent the intra-aortic balloon pump has a central or main pumping balloon, and one or two valve balloons positioned on one or both sides of the main pumping balloon. The associated catheter has a separate lumen for each of the balloons, and the drive unit has to control the pressure separately for each of the balloons, i.e., each of the two or three associated lumens requires a separate gas conduit. The valve balloons assist in the directionality of blood flow, so that the flow is directed toward the heart during diastole. In some instances, the pumping balloon must be inflated more than once during systole. This arrangement can approximate a peristaltic action by inflating multiple times during each coronary cycle. However, the rather complex pumping cycle can be difficult to implement, and the need for the distal and proximal end balloons restricts the size of the main pumping balloon, thereby limiting the amount of stroke enhancement. Also, the need for a separate conduit to inflate and deflate the chambers in the described fashion increases the complexity of the device and increases the size of the catheter, making it less safe. It also requires a specially designed extracorporeal inflation/deflation device. All of this makes the design highly impractical.
Accordingly, it is an object of this invention to provide a minimally invasive, cost-effective, temporary left-ventricular assisting device to augment cardiac output in an acutely failing heart.
It is another object to provide an IABP that inflates and deflates through a single lumen of the associated catheter.
It is a further object to provide an IABP with a catheter that is compatible with existing IABP equipment.
In accordance with an aspect of the present invention, a segmented peristaltic intraaortic balloon pump employs a catheter that is adapted to be inserted into the aorta of a patient, and has a lumen adapted for passage of helium or another suitable a drive gas. A segmented balloon is positioned on the distal portion of the catheter and has three or more chambers in succession. In a preferred embodiment, first, second, and third chambers are arranged from distal to proximal on the catheter, and there are apertures formed in the catheter for communicating drive gas between the lumen and the chambers, respectively. This permits gas in the lumen to inflate and deflate the first, second and third chambers such that said chambers inflate in sequence from distal to proximal and then deflate in sequence from distal to proximal. A pumping device outside the patient""s body is connected to the lumen at a proximal end of the catheter. The pumping device pumps the gas into and out from said lumen to inflate during systole and deflate during diastole. In a preferred mode the three (or more) chambers are successively larger in the direction from distal to proximal, i.e., with the smallest chamber being closest to the aortic root. Also, the apertures or openings from the lumen to the chambers are largest for the most distal, i.e., first, chamber and then progressively smaller for the second chamber, third chamber, and so on. This arrangement ensures that the first chamber will inflate first, then the second, and then the third, which causes peristaltic pumping toward the lower arteries. Similarly, the first chamber will deflate first, followed by the second chamber, and then the third chamber. This creates a negative pressure just prior to systole, to alleviate back pressure on the left ventricle, and relieves pumping load on the left ventricle. This also avoids flow towards the aortic root, which can cause problems if the patient""s heart has aortic regurgitation.
The catheter can be inserted percutaneously through the iliac artery into the thoracic descending aorta. Helium is pumped into and out of the outer lumen or the catheter to the multiple inflatable chambers, while the inner lumen is used for pressure transduction. The chambers inflate in sequential order during early diastole, starting with the chamber most proximal to the aortic root to the chamber most distal from the aortic root. This order of balloon inflation pushes blood downstream in peristaltic fashion. The chambers will also deflate in a sequential order just prior to systole starting with the chamber most proximal to the aortic root. This sequence of deflation will generate a negative pressure in the aorta directed at the ventricle prior to systole, thus decreasing cardiac work load. The catheter inflation/deflation and timing can be accomplished using existing IABP equipment.
The above and many other objects, features, and advantages of this invention will become apparent to persons skilled in the art from the ensuing description of a preferred embodiment, which is to be read in conjunction with the accompanying Drawing.